Electric fields may be beneficial in providing therapies related to a number of medical conditions. Many known therapies utilize application of electric fields to patients. These electric fields may be AC or DC fields that are applied locally to a small, precise location of a patient's body, or to larger regions that may include entire organs.
Implantable medical devices, such as cardiac pacemakers or cardioverter-defibrillators, include leads that deliver therapeutic electrical stimulation to the heart in the form of pacing, cardioversion or defibrillation pulses. The pulses are delivered to the heart via electrodes disposed on the leads, typically near distal ends of the leads. The leads serve to position the electrodes with respect to various cardiac locations to deliver electrical stimulation pulses to appropriate locations. Leads are also used for sensing purposes, or both sensing and stimulation purposes.
In addition, implantable leads are used in neurostimulation devices for deep-brain stimulation, spinal cord stimulation, sacral stimulation, and gastrointestinal tract stimulation. Leads are also used with a wide variety of other medical devices including, for example, devices that provide muscular stimulation therapy, devices that sense chemical conditions in a patient's blood, gastric system stimulators, implantable lower colon stimulators, e.g., in graciloplasty applications, implantable drug or beneficial agent dispensers or pumps, implantable cardiac signal loops or other types of recorders or monitors, implantable gene therapy delivery devices, implantable incontinence prevention or monitoring devices, implantable insulin pumps or monitoring devices, and the like. In summary, medical leads can be used for sensing purposes, stimulation purposes, drug delivery, and so forth. These exemplary uses of implantable leads typically involve energizing the leads for relatively short periods of time.
Implanted electrodes function in a harsh biological environment and are often exposed to a variety of fluids. Over time, sustained electric fields may cause electro-chemical reactions to occur at the electrodes, resulting in corrosion. Corrosion can be particularly problematic in environments that contain biological fluids, such as water. Electrode corrosion has generally limited the use of electric fields for therapy to short, durational, or intermittent electrical fields.